To make a long story very short: Copenhagen, very walkable if you are moderately fit, but shuttle buses should be provided; Stockholm, depands where you are berthed but walkable for the old town to the Vasa museum (not to be missed), Helsinki again depands where you are berthed, but a nice city to walk round. Scandinavian prices are about on par with Britain (expensive!) In St Petersburg the easy, but more expensive, option is a ship's excursion, but other operators e.g. Denrus are available. Don't try to do this one one your own. Tallin is lovely, take the bus in to the old town and try to be early before it gets too crowded, you can go round the shops afterwards, linen is inexpensive. If you have a port in Poland prices are very reasonable, especially lead crystal. I've not been to Riga so can't comment. Have a lovely trip.